Unlike children and adults, infants (including newborns) are not capable of communication by means of words. Therefore, the state of an infant has to be conjectured only through observation.
Conventionally, a device for thus observing the state of an infant has been proposed (see, for example, Patent document 1: Japanese Translation of PCT Publication No. 2001-516253). In Patent document 1, a nose mask type pneumotachograph is used for a newborn to obtain its respiratory waveform, and various kinds of analyses are conducted based on the respiratory waveform.
Another possible method is to take an electrocardiogram from a newborn and conduct various kinds of analyses based on the electrocardiogram as is done for an adult. (see, for example, Patent document 1: claim 10, p. 17 “Summary of the Invention”, and the third line from the bottom to the final line of p. 25).